1. Field of the Invention
This invention relates to fluid handling, more specifically to a subterranean, plastic, box for fluid distribution, such as is used in septic tank systems and geographical drainage, which has seals for receiving and sealing around subterranean pipes.
2. Description of the Prior Art
It is important to maintain a secure and watertight seal at a first stage between a fluid distribution box and the seal means at an opening through the box wall, and at a second stage between the seal means and the pipe which is connected to the box by entering through the seal means.
The strength and watertightness of each of the two stages is attacked by physical impact against the pipe and seal from backloading of soil into the trench in which the box and pipes are buried, and by heaving and settling of soil around the wall openings and the pipes during the 10, 15, or more years that the subterranean distribution system must last.
Installers and manufacturers are well aware of the above problem of providing a long time and secure seal between an underground box and the pipe with which it is connected. Many inventions which attempt to solve the problem for concrete and for plastic boxes have been patented.
Concrete boxes have thick walls and a high weight to volume ratio. They are seldom subjected to upward floating movement from soil water displaced by the box during rises in the water table, and tend to be stable if properly bedded. Effective two stage seals have been developed for the concrete box and have been contributing a solution to the problem for many years.
Although a solution for the described seal problems in concrete boxes has been sold and in public use for many years, a good solution for the more severe seal problem in plastic boxes is still needed.
A septic system concrete septic tank and distribution box, for example, U.S. Pat. No. 5,286,040, patented Feb. 15, 1994 by Norman Gavin describes an elastomeric seal which includes, at the first stage, an integral annular flange on the cylindrical outer body portion of the seal. The flange extends generally radially outwardly and is adapted to be embedded in the cast cementitious material about an opening through a wall of a concrete distribution box during casting of the box to secure the seal in position in the opening. The cement surrounds the flange and cylindrical outer body for substantially the full axial length of the body, forming a watertight seal between the wall and the body.
At the second stage, the elastomeric seal has a frustoconical wiper blade which has a knock out web at its smaller diameter end portion. The knock out web includes two weakened narrow annular portions of different sizes, on different centers.
U.S. Pat. No. 4,805,920, patented Feb. 21, 1989, and U.S. Pat. No. 4,732,397, patented Mar. 22, 1988, by Norman Gavin also describe a frustoconical seal which includes an integral annular flange that extends generally radially outwardly and is adapted to be embedded in the cast cementitious material about the opening through the wall of the concrete box during casting of the box.
Plastic boxes have relatively thin walls. They are more likely to be dislodged by changes in the water table and shifts in soil.
U.S. Pat. No. 4,663,036 patented May 5, 1987 by Strobl, Jr. et al., describes a generally flexible seal for an opening through the wall of a plastic distribution box.
The seal includes a cylindrical outer wall having a pair of annular flanges which extend generally radially outwardly and are adapted to clamp between them, the box wall immediately forming the opening. The flanges are inclined slightly toward one another, and the cylindrical wall between them includes an annular radially outwardly extending bead. The pair of annular flanges clamp and sealingly engage the box side wall adjacent to the opening, and the bead contacts the inward edge of the wall surrounding the opening when the seal is snap-fitted into the opening.
A frustoconical shaped wiper blade member which extends inwardly from one end of the cylindrical outer wall forms a pipe-receiving opening of predetermined size through the blade member. The blade member engages and seals against a pipe that is suitably sized to fit the opening through the blade member when the pipe is inserted through the pipe-receiving opening of the wiper blade member.
The inclining of the flanges slightly toward one another contributes to sealing between the seal body and the wall of the box when the inserted pipe rotates slightly out of axial alignment with the axis of the cylindrical outer wall.
An excessive angle with respect to the axis of the cylindrical wall, of a pipe inserted through the pipe-receiving opening, can cause the snap-fitted seal member to pop out of the box wall opening. Soil hydraulic and shifting forces also can have a deleterious effect upon the long time reliability and quality of the two stages of sealing.
A twist-in seal for a plastic distribution box is made by American Manufacturing Co. Inc., Manassas, Va. The seal 20, shown in FIGS. 1-4, labeled PRIOR ART, has a pair of annular flanges 24 and 28 which extend generally radially outwardly and are adapted to clamp between them, wall 32 of a plastic distribution box, immediately where it forms opening 36. Flange 24 is continuous, flexible and inclined toward flange 28 so that surface 38 sealingly contacts wall 32 when wall 32 is clamped between flanges 24 and 28. Flange 28 formes a plurality of lugs 44 which have inclined lead faces
Seal 20 is installed in the box wall 32 opening 36 which has radially inwardly extending portions 54 by orienting seal 20 so that lugs 44 clear portions 54 when flange 28 is inserted through opening 36, then rotating seal 20 so that lead faces 46 engage portions 54 and draw surface 38 of flange 24 sealingly against wall 32.
Axially extending grip bars 58 are provided for use by an installer to aid in twisting the seal in place against the counterrotational friction between the flanges and the wall.
Frustoconical flexible seal wall 62 forms opening 64 for receiving a pipe of proper diameter so that wall 62 seals against the outer surface of the pipe. The installer must take care not to rotate the pipe after installation, as there is a chance that the pipe may rotate the seal toward an unlocking position or to one of reduced sealing force between flange 24 and wall 32.
U.S. Pat. No. 5,361,799, patented Nov. 8, 1994 by Chilton et al, describes a subterranean, plastic, preformed waste water access fitting comprising a hollow body that has a vertical extension and two horizontal extensions. The vertical extension is sealed over at the top, and can be cut off at the top in order to obtain access to the inside of the body for maintenance or to insert a standpipe. Each of the horizontal extensions are formed of connected segments of decreasing outer diameter with a cutting guide on each segment. The segments can be cut to mate with various diameters of pipe. Referring to FIG. 5, PRIOR ART plastic distribution boxes 70 and 72 have clamped-in seals 74, 76, 78 and 80. Box 72 rests on box 70, but can not be shipped fully nested in box 70 when the seals are installed in the boxes because clamp rims 82 and 84, and frustoconical wiper blades 86 interfere with full seating of one box in the other. It is not practical, therefore, to ship the boxes with the seals installed. The seals and boxes may be shipped separately and, the seals installed in the boxes at the construction site. An inventory of different size seals may be shipped in order to be able to install a seal that will fit one of a predetermined variety of smooth and corrugated pipes of different diameter.